Skip to main content

Full text of "Text Book Of Mechanical Engineering"

See other formats

1140                           Appendix VL

delivered under pressure to the bearing pipes cc, and then by the
channels D D E in the crank shaft to the crank pins. From the
crank-pin journals it travels through pipes FFF to the gudgeons,
and finally to the crosshead slides, whence it returns to the tank.
Two important things have been secured : (i) the oil has been
fed under a pressure of 10 Ibs. per sq. in. to all the moving pins
and journals, so that the shock of reversal is taken by a fluid
which is elastic through leakage but yet highly resistant, and
(2) the engine has been efficiently lubricated. Practically any
1 knock/ however severe, can be taken up by this method, though
f ,                      of course lack of balance is always finally transferred to the

i                      foundations and felt as vibration.    The  steam first enters the

i                      chamber K, and is distributed to the high-pressure cylinder H,

from which it is exhausted to the low-pressure cylinder j.    The
governor K is of the same type as that on p. 893.

1                           P. 640.    Link Motion.

;!                           Equivalent Crank.—Let OD, Fig. 1007, be an engine-crank,

A                      and o A, o B two eccentric cranks, whose radii are r and r1 and

4                      whose advance angles are a and a: respectively.    It is required

||                      to find a single crank that will give the same motion to c that the

'|!                      combined cranks will give. Complete the parallelogram o A B E, and

I                      the diagonal R will be the equivalent crank.     For, dropping per-

Ipendiculars to Ax ^ EX ;   OAI = EIEI and therefore the motion
due to R will equal o BX + o Aa or that due to the cranks r and r±
taken together.    If A and B be now coupled to link a br whose
j                      mid point is c; the slide d will only receive half the travel due to

1                      equivalent crank R.

|                           In Fig. 1008 we require a crank that will give the relative

I                      motions of the slides d e as caused by the cranks r and rlt   Join

I                      A B and complete the parallelogram E B, when R will be the

|                      required   crank.     For  o Er = AJ BJ,  which   is   the   differential

motion OAi-OBi excepting for change of sign, which puts OE

in the left quadrant.

In Fig. 1009 two cranks are connected to a link where the


valve spindle c is not centrally adjusted,   c will receive —


of A'S motion plus — of B'S motion.    To find the equivalent